This invention relates generally to marine propulsion systems, and has particular reference to a novel dual engine, twin propeller marine propulsion system for cruising boats which is considerably more efficient than conventional twin engine power plants.
As is well understood by those familiar with ship and boat handling, a twin engine, twin propeller propulsion system has certain advantages over a single engine system. Thus, the twin engine system usually provides greater power and is more reliable; if one engine fails there is another one to fall back on. The twin engine system also makes a ship or boat more maneuverable since by having one propeller turning in the forward direction and the other in the reverse direction the boat can be "twisted", i.e. turned with a very short turning radius.
In conventional twin engine propulsion systems, the engines are mounted side by side and are the same make and power, one of the engines having a left hand turning propeller and the other a right hand turning propeller. Unfortunately, in these systems there is a great deal of power wasted because, due to basic combustion engine design, optimum efficiency is obtained only in a relatively narrow R.P.M. band. Also, because cruising boats must be designed and powered to safely meet severe sea and weather conditions, the engines have far more power than is normally needed. Oversized engines in fast planing hull type boats also waste power because the boats travel at slow displacement and semidisplacement speeds most of the time. When very powerful engines are used to propel boats at slow speeds not only is there poor fuel economy but maintenance problems increase, e.g. spark plugs foul, cylinders and valves carbonize, etc.
In efforts to solve some of the problems noted above, various other types of propulsion systems have been proposed. One of these provides for a single inboard engine with a power generator nearby that can be manually connected to the propeller shaft if the main engine fails. In Europe a system has been used in which a small engine with its own transmission and propeller is mounted next to a centrally located main engine. Again, the small engine is only for an emergency as its use is not efficient. Another system that has been proposed is one in which identical twin engines are coupled to a single propeller. This provides insurance in the event that one engine fails but the system has none of the other advantages of a twin engine, twin propeller system and is quite inefficient in operation.
The closest prior patent known to the applicant is U.S. Pat. No. 1,019,283 to E. Surcouf. The Surcouf patent discloses a propulsion system for airships in which a pair of engines, one having substantially more power than the other, are coupled to a pair of propeller shafts in such a manner that the engines can simultaneously drive both propellers, either engine can drive either one of the propellers, or either engine can drive both propellers. The Surcouf patent does not teach the athwartships shaft, transmission and clutch arrangement of the present invention, and in the invention it is not desired to have the two engines in operation simultaneously. Other prior art patents developed in a preliminary search are U.S. Pat. Nos. 1,781,656; 1,802,931; 2,501,617 and 3,155,070.